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Beocenter 9500 CD outputs increasing static noise

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Martin
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Martin posted on Fri, Feb 26 2021 6:15 PM

Hi!

The CD player in my Beocenter 9500 was having trouble reading the CD, so I replaced the famous C2103 capacitor from the kit found at Beoparts Shop which solved that problem!

At that time, I did not change the other capacitors included in the kit, since I figured "don't fix what's not broken".

However, after playing any CD for only a few minutes, a faint static noise can be heard which slowly increases in volume and the sound becomes more and more distorted at the same time. After only a minute or so, the static takes over completely. It is the same when listening via headphones as well as via Powerlink speakers.

Switching to any other source shows no hint of the problem. And switching back to the CD after a minute, the static has decreased but starts building again which made me think it is probably one of the other capacitors fault.

After this, I replaced the other five capacitors from the kit but unfortunately, the behaviour is unchanged.

Do you have any suggestions what could cause this? Is it likely another component on the CD board or are there parts on any other board that only the CD uses in the output? On Diagram C, it says "Power Supply and Output Ampl. for 16 bit CD version". Could that be involved? Or PCB31 "Decoder"?

Any advice where to start looking is appreciated!

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TheTinman
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Verified by Martin

@Martin,  try some freeze spray when it acts up.  This has worked well for me finding thermal faults, which it sounds like you have.

Martin
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Answered (Verified) Martin replied on Thu, Mar 18 2021 4:47 PM
Verified by Martin

I tried the freeze spray. I barely started spraying on the TDA1541A DAC chip and the noise immediately stopped. Waiting a minute again to have the noise start, it actually stopped when I put my (colder) finger on the chip!

I have now put on a heat sink to see if this is enough of a fix!

Googling about this, it seems that it is not uncommon.

Here they mention my exact symptom, "Classic TDA1541 failure mode I'm afraid. Overheating after a short time of operating and steadily increasing levels of distortion!"

https://www.diyaudio.com/forums/digital-source/97341-tda-1541-problem-ping-jocko-homo-print.html

So, this might be a failure that will get increasingly worse and that I am only buying myself some extra time. But if that is the case, I will look for a "new" TDA1541A chip and maybe even solder a socket to the board?

I will update this post when I have done some more long term testing. Thanks all! Smile

Martin
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Answered (Verified) Martin replied on Sat, Apr 3 2021 11:41 AM
Verified by Martin

I replaced the entire decoder board which contains the TDA1541A chip with one from a spare Beocenter 9500. This fixed the problem and the 1541 chip is noticeably cooler to the touch!

The filter chip on the same board always run rather hot, so I put small heat sinks on both these chips. Can’t hurt right?

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Spassmaker
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Hi Martin

Unusual after recapping the servo board.

maybe the issue is to search somewhere else.

Have you tried some other CD´s?

Did you touch any trimmers on the servo board?

Did you measure the laser current as in the service manual discribed?

Kind regards

Christian

Martin
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Martin replied on Sun, Feb 28 2021 6:33 PM

Thanks for your reply!

My guess is that this is not laser related at all. It tracks records just fine. I can search and skip tracks and it sounds fine at first. It sounds almost as if I had a radio with no channel tuned in and slowly mixing it in with the CD sound to the point where it takes over completely over the course of 30 seconds or so. And increasingly, the CD sound becomes distorted as well.

Can it still be a laser related thing you think?

No components have been touched except the replaced capacitors.

I have not measured anything related to the CD player.

Maybe something on the decoder PCB?

Martin
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When the static noise has started, I can also hear a quiet "pop" when changing tracks and when pressing Stop, I can hear that the part of the noise is fluctuating at the same speed as the CD is rotating, if you know what I mean. It changes depending on which track I play/how quick the motor operates.

Can this be of any help indicating what part of the decoder board might be the problem?

It takes a few minutes before the noise starts, so I guess it is related to the temperature of the components somehow. The ICs are quite hot to touch. I can only barely keep the upper side of my finger on them. Is that normal?

I have inspected the board for solder cracks or cold solder joints and only found one that was only slightly suspicious. I reflowed it just to be certain.

Orava
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Orava replied on Mon, Mar 8 2021 7:21 AM

Wires from CD to decoder board?

 blah-blah and photographs as needed

Spassmaker
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Hi Martin

If it' s possible for you please try to measure the laser current regarding to the service manual.

If it's out of specs ( 50mV) try to adjust with the related trimmer, but very carefully because the adjustment is very sensitive.

Kind regards

Christian

Dillen
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I wouldn't adjust anything. It seems to track fine. I don't think it's a laser-related problem.
Check for cracked solder joints (depending on drive version) at the voltage regulators on the decoder board and
at the large filter capacitors in the power supply - and also the relay in the power supply and (again depending on version) at the small relay board
in front of the decoder board.

Martin  

Martin
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Thanks for your replies,

@Orava - I will check the wires. But since it always sounds good when I start to listen and also if I take a minute break after hearing the static, it sounds fine again for a while I am not sure if it could be a cable problem?

 

@Dillen - I don't see anything suspicous on the voltage regulators but I can certainly reflow them just to be sure! I will inspect the relays as well, though they are working well it seems.

Also, are any of the large filter capacitors in the power supply used only for this board (since I notice no problems on any other source)? Or can it be that this board draws more current than the others (which the warm ICs would suggest) and therefore puts a larger strain on the capacitors and traces in the power supply chain?

TheTinman
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Verified by Martin

@Martin,  try some freeze spray when it acts up.  This has worked well for me finding thermal faults, which it sounds like you have.

Martin
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Martin replied on Wed, Mar 17 2021 9:53 AM

Thanks @TheTinman, I will try to find some spray and do some testing!

Martin
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Answered (Verified) Martin replied on Thu, Mar 18 2021 4:47 PM
Verified by Martin

I tried the freeze spray. I barely started spraying on the TDA1541A DAC chip and the noise immediately stopped. Waiting a minute again to have the noise start, it actually stopped when I put my (colder) finger on the chip!

I have now put on a heat sink to see if this is enough of a fix!

Googling about this, it seems that it is not uncommon.

Here they mention my exact symptom, "Classic TDA1541 failure mode I'm afraid. Overheating after a short time of operating and steadily increasing levels of distortion!"

https://www.diyaudio.com/forums/digital-source/97341-tda-1541-problem-ping-jocko-homo-print.html

So, this might be a failure that will get increasingly worse and that I am only buying myself some extra time. But if that is the case, I will look for a "new" TDA1541A chip and maybe even solder a socket to the board?

I will update this post when I have done some more long term testing. Thanks all! Smile

Martin
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Martin replied on Thu, Mar 18 2021 8:12 PM

It was unfortunately not enough to use a heatsink, so I am now looking for a working TDA1541A chip to replace mine with.

If anyone have one for sale, please let me know! Smile

Martin
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Answered (Verified) Martin replied on Sat, Apr 3 2021 11:41 AM
Verified by Martin

I replaced the entire decoder board which contains the TDA1541A chip with one from a spare Beocenter 9500. This fixed the problem and the 1541 chip is noticeably cooler to the touch!

The filter chip on the same board always run rather hot, so I put small heat sinks on both these chips. Can’t hurt right?

TheTinman
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Had the same problem in a ROTEL CDP.  Replaced the TDA1541.... TWICE!  Sadly there are plenty of "bad" chips out there.  But eventually got a good one.

I should note that we are seeing (now) an increasing IC and transistor deterioration in old gear.  This seems more a matter of AGE, not USE.

Martin
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True! And the TDA1541A is getting rather expensive on the second hand market...

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